Abstract
We have elucidated that cyclic electron-flow around PSI (CEF-PSI) functions with photosynthetic linear electron-flow, and in the formation of ATP and the induction of non photochemical quenching (NPQ) of chlorophyll fluorescence, through the formation of ΔpH across thylakoid membranes. The facts are follows; (1) Increase in light intensity enhanced CEF-PSI and NPQ even after photosynthesis saturated. (2) Lowering Ci enhanced CEF-PSI and NPQ. (3) CEF-PSI shows the positive relationship with NPQ. (4) Transplastomic tobacco having a large amount ferredoxin in chloroplasts showed a larger CEF-PSI, compared to wild type. (5) Transplastomic tobacco showed an enhanced NPQ. (6) Transplastomic tobacco did not enhance photosynthesis. These results show the shift of redox state of chloroplasts to the reduced conditions induces CEF-PSI to drive NPQ, which protects plants from their photoinhibition. And further, the intrinsic activity of CEF-PSI in wild type is enough to support net CO2 assimilation.
